1. Field of the Invention
This invention generally relates to a sector drive mechanism, and more particularly, to a sector drive mechanism that can drive a sector efficiently by use of an electromagnetic actuator.
2. Description of the Related Art
In recent years, cameras have been computerized, and a sector is driven by use of an electromagnetic actuator. In this type of camera, it is desirable that the sector such as a shutter blade or aperture blade may be retained even when no current is applied. For instance, Japanese Patent Application Publication 2001-61268 (hereinafter, referred to as Patent Document 1) discloses the electromagnetic actuator having a magnetic member, which applies a locking force so that a rotor comes to a given position without swinging when the coil is not active. Such electromagnetic actuator enables the rotor to stop at an accurate position when the motor stops, and also enables to suppress the power consumption.
With respect to a sector drive apparatus for use in a camera, it is desirable that a drive portion such as the aperture blade or the shutter blade may be driven quickly, when necessary. For instance, Japanese Patent Application Publication 11-18492 (hereinafter, referred to as Patent Document 2) proposes a technique of driving the electromagnetic actuator quickly in a two-phase excitation method to a position near a final stopping position of an aperture open and close mechanism, and then driving in a one-two-phase excitation method for the remaining small portion to the final stopping position. With this proposal, it is possible to narrow the aperture to a given aperture value for a short period, reduce the time lag, and increase the accuracy of aperture value at the completion of aperture.
The electromagnetic actuator disclosed in the above-described Patent Document 1, however, has to additionally arrange a magnetic member so as to apply the locking force to the rotor. So, another member is added to the stator and a complex processing is implemented. This complicates the structure of the motor, resulting in a problem of increased production costs. The drive technique disclosed in the above-described Patent Document 2 proposes the technique for accurate position control, when the electromagnetic actuator is driven in the conventional and general two-phase excitation. Nevertheless, in the drive technique disclosed in Patent Document 2, the electromagnetic actuator is changed to the one-two-phase excitation method from the two-phase excitation method, while the aperture open and close mechanism is being driven. Therefore, there is the problem in that data creation and control systems are complicated and the costs are increased.